The instant invention relates to a process for forming a deposit on the surface of a metallic or conductive surface. The process employs an electrolytic process to deposit a mineral containing coating or film upon a metallic, metal containing or conductive surface.
Silicates have been used in electrocleaning operations to clean steel, tin, among other surfaces. Electrocleaning is typically employed as a cleaning step prior to an electroplating operation. Using xe2x80x9cSilicates As Cleaners In The Production of Tinplatexe2x80x9d is described by L. J. Brown in February 1966 edition of Plating; hereby incorporated by reference.
Processes for electrolytically forming a protective layer or film by using an anodic method are disclosed by U.S. Pat. No. 3,658,662 (Casson, Jr. et al.), and United Kingdom Patent No. 498,485; both of which are hereby incorporated by reference.
U.S. Pat. No. 5,352,342 to Riffe, which issued on Oct. 4, 1994 and is entitled xe2x80x9cMethod And Apparatus For Preventing Corrosion Of Metal Structuresxe2x80x9d that describes using electromotive forces upon a zinc solvent containing paint; hereby incorporated by reference.
The instant invention solves problems associated with conventional practices by providing a cathodic method for forming a protective layer upon a metallic or metal containing substrate. The cathodic method is normally conducted by immersing an electrically conductive substrate into a silicate containing bath wherein a current is passed through the bath and the substrate is the cathode. A mineral layer comprising an amorphous matrix surrounding or incorporating metal silicate crystals can be formed upon the substrate. The characteristics of the mineral layer are described in greater detail in the copending and commonly assigned patent applications listed below. The mineral layer can impart improved corrosion resistance, increased electrical resistance, among other properties, to the underlying substrate.
The inventive process is a marked improvement over conventional methods by obviating the need for solvents or solvent containing systems to form a corrosion resistant layer, e.g., a mineral layer. In contrast, to conventional methods the inventive process is substantially solvent free. By xe2x80x9csubstantially solvent freexe2x80x9d it is meant that less than about 5 wt. %, and normally less than about 1 wt. % volatile organic compounds (V.O.C.s) are present in the electrolytic environment.
The inventive process is also a marked improvement over conventional methods by reducing, if not eliminating, chromate and/or phosphate containing compounds. While the inventive process can be employed to enhance chromated or phosphated surfaces, the inventive process can replace these surfaces with a more environmentally desirable surface. The inventive process, therefore, can be xe2x80x9csubstantially chromate freexe2x80x9d and xe2x80x9csubstantially phosphate freexe2x80x9d and in turn produce articles that are also substantially chromate free and substantially phosphate free. By substantially chromate free and substantially phosphate free it is meant that less than 5 wt. % and normally about 0 wt. % chromates or phosphates are present in a process for producing an article or the resultant article. In addition to obviating chromate containing processes, the inventive method forms a layer having greater heat resistance than conventional chromate coatings. The improved heat resistance broadens the range of processes that can be performed subsequent to forming the inventive layer, e.g., heat cured topcoatings, stamping/shaping, among other processes.
In contrast to conventional electrocleaning processes, the instant invention employs silicates in a cathodic process for forming a mineral layer upon the substrate. Conventional electro-cleaning processes sought to avoid formation of oxide containing products such as greenalite whereas the instant invention relates to a method for forming silicate containing products, i.e., a mineral.
The subject matter of the instant invention is related to copending and commonly assigned Non-Provisional U.S. patent application Ser. Nos. 08/850,323; 08/850,586; and 09/016,853 (EL001RH-6, EL001RH-7 and EL001RH-8), filed respectively on May 2, 1997 and Jan. 30, 1998, and Ser. No. 08/791,337 (Attorney Docket No. EL001RH-4 filed on Jan. 31, 1997) in the names of Robert L. Heimann et al., as a continuation in part of Ser. No. 08/634,215 (filed on Apr. 18, 1996) in the names of Robert L. Heimann et al., and entitled xe2x80x9cCorrosion Resistant Buffer System for Metal Productsxe2x80x9d, which is a continuation in part of Non-Provisional U.S. patent application Ser. No. 08/476,271 (filed on Jun. 7, 1995) in the names of Heimann et al., and corresponding to WIPO Patent Application Publication No. WO 96/12770, which in turn is a continuation in part of Non-Provisional U.S. patent application Ser. No. 08/327,438 (filed on Oct. 21, 1994), now U.S. Pat. No. 5,714,093.
The subject matter of this invention is related to Non-Provisional patent application Ser. No. 09/016,849 (Attorney Docket No. EL004RH-1), filed on Jan. 30, 1998 and entitled xe2x80x9cCorrosion Protective Coatingsxe2x80x9d. The subject matter of this invention is also related to Non-Provisional patent application Ser. No. 09/016,462 (Attorney Docket No. EL005NM-1), filed on Jan. 30, 1998 and entitled xe2x80x9cAqueous Gel Compositions and Use Thereofxe2x80x9d, now U.S. Pat. No. 6,033,495. The disclosure of the previously identified patents, patent applications and publications is hereby incorporated by reference.